Yes, user applications making use of the Oracle provided dbms_lock package is the likely source of the statements in question. Note that normally user processes do not update the rdbms base tables, i.e, tables owned by user SYS. So unless someone is doing something that is unsupported by Oracle then this SQL is from Oracle's internal processing.

Mark, DBMS_LOCK.SLEEP has nothing to do with it. It is used in each iteration while references to DBMS_LOCK_ALLOCATED start 5 min after startup. I can repeat the test without using DBMS_LOCK.SLEEP for a clean experiment: